Pouring technique for continuous casting



Dec. 4, 1962 R. BAlER 3,066,364

POURING TECHNIQUE FOR commuous CASTING Original Filed March 26, 1958 4 Sheets-Sheet 1 INVENTOR. RICHARD 8.4/51? BY 6 MM 3: M

ATTORNEY Dec. 4, 1962 R. BAIER 3,066,364

POURING TECHNIQUE FOR CONTINUOUS CASTING Original Filed March 26, 1958 4 Sheets-Sheet 2 r l I H I I I H g I '1 l I ,"i 13 I I ,l H: :H I I l 60 fi h 15' NH l J u INVENTOR.

RICHARD BA/ER ATTORNEY Dec. 4, 1962 R. BAIER POURING TECHNIQUE'FOR CONTINUOUS CASTING Original Filed March 26, 1958 4 Sheets-Sheet 3 m 9m m n 2/ m m Z w /wz M w m Z d 70 4 054 m a A H C I ll m \V I ll] JII Ha v. M w 0%vl ol Dec. 4, 1962 R. BAIER POURING TECHNIQUE FOR CONTINUOUS CASTING 4 Sheets-Sheet 4 Original Filed March 26, 1958 INVENTOR RICHARD 5/1/15)? A TTOENEY Patented Dec. 4:, l62

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9 Claims. (Cl. 22-572) The invention relates to the continuous casting of metals and more particularly to pouring techniques for the continuous casting of copper billets.

This application is a division of application Serial No. 724,114, filed March 26, 1958.

According to a preferred form of the invention, the pouring mechanism comprises a pouring ladle having an enlarged reservoir at the back and a siphon tube at the front. The siphon tube has at its back a strainer immersed in the molten metal held in the ladle; and at its front an overflow cup for sealing the discharge tip of the siphon to prevent loss of suction when starting up a pouring operation. A shroud surrounds the siphon to aid in melting out the siphon if metal should be accidentally frozen therein.

A special support is provided for the pouring ladle; this support permits tilting the ladle, front-to-back, in a ertical plane; raising and lowering the ladle along a vertical axis; and swiveling the ladle about a vertical axis. This special support is useful in carrying out the starting-up technique, which comprises flowing the molten metal into a waste pot to obtain the proper flow rate before swinging the ladle over the mold to start the continuous casting operation.

General objects of the invention are to cast metals, particularly phosphorized copper billets, at greatly increased linear rates; to produce castings having superior surface and internal characteristics; to provide a pouring mechanism and pouring technique by which the pouring rate may be very closely controlled and maintained; to pro vide methods and equipment for continuous casting having one or more of the above recited features and capable of accomplishing one or more of the aforesaid objects.

Other objects and features of the invention will be more apparent from the following description and claims when considered with the accompanying drawings in which:

FIG. 1 is an elevation of the casting system showing holding furnace, pouring ladle, siphon, mold, mold carriage, and mechanism for withdrawing the cast product, certain parts being shown in section;

FIG. 2 is a plan view of FIG. 1 showing how the pouring ladle-siphon assembly may be swung clear of the mold for starting purposes; certain parts are omitted for simplicity of illustration;

FIG. 3 is an elevation of the siphon showing its mounting on the ladle and showing its relationship to the mold during the casting operation, certain parts being shown in section;

FIG. 4 is a section on the line 4-4 of FIG. 3 illustrating the darn across the shroud for permitting a head of molten metal to be built up in the ladle to start metal flow just prior to swinging the siphon over the mold;

FIG. 5 is a section on the line 5-5 of FIG. 3 further illustrating the siphon construction;

FIG. 6 is a section on the line 6-6 of FIG. 3 showing how the front end of the shroud is constricted around the siphon tube;

FIG. 7 is a section on the line '77 of FIG. 3 illustrating the overflow cup which seals the discharge tip of the siphon when starting metal flow;

FIG. 8 is a detail of the steatite bushing in the cup orifice;

FIG. 9 is an elevation, mostly in section, of the billet mold;

FIG. 10 is a half plan section, taken on the line lll-1tl of FIG. 9, half of the mold being omitted for simplicity of illustration;

FIG. 11 is a cross section taken through a tube assembly on a larger scale; on line 11-11 of FIG. 9.

In tl e accompanying drawings and in the description forming part of this specification, certain specific disclosure of the invention is made for purposes of explanation, but it will be understood that the details may be modified in various respects without departure from the broad aspect of the invention.

Referring to the drawings and more particularly to FIGS. 1 and 2, the system of casting, utilizing the invention, will be first only generally outlined, after which more detailed description of the method and apparatus will be given.

General Description A melting furnace (not shown) supplies holding furnace 10 with the molten metal to be cast. The furnace 10 supplies pouring ladle 11 which in turn supplies siphon 12; the latter supplies mold 13 which is mounted on mold platform 1'4- which in turn is mounted for vertical reciprocation on carriage t5.

Carriage 15 is movable horizontally on tracks 36 from over tank Ztl, to provide access to the product after it is cast, as hereinafter explained more in detail. It will be understood that a stationary working floor (not shown) is located on opposite sides of the tracks 16, at the same level as the tracks 16, on which workmen may walk during pouring.

For effecting the casting operation, a hydraulic starting and lowering mechanism is located within and under tank 2%; this comprises a starting plug 17 mounted on platform 18 which in turn is supported on piston 19 which has Working relation with a hydraulic cylinder 22 located below water tank 20. The upper end of plug 17 is screwthreaded as indicated at 21.

It will be understood that the starting platform 18, as shown in FIG. 1, is in approximately its uppermost position with the starting plug 17 projected up inside the mold 13. The starting plug 17 forms the bottom closure of the mold when initiating the pour. As molten metal is fed into the mold, it freezes around threads 21 and the frozen product is pulled downwardly at uniform speed into the tank 20 by the hydraulic arrangement. Upon completing the casting operation, the starting plug is disengaged from the cast product by relative rotation, screw threads 21 permitting easy disengagement.

The tank 26} may extend below the top surface of the mold a distance corresponding to the desired length of the cast product, which may be as much as 27 feet long;

in such case the hydraulic cylinder arrangement must extend below the mold top more than twice this amount, or over 54 feet, to accommodate the piston 19 in its fully retracted position.

Alternately, the hydraulic pulling mechanism may be replaced by a conventional roll drive, cut-off mechanism and handling equipment, such as disclosed in Betterton and Poland Patent No. 2,291,204, granted July 28, 1942.

The holding furnace shown is an upright low frequency induction furnace rotatable about a horizontal axis and having a pouring spout 25. It may receive molten metal through a launder or a bull ladle (not shown) from a suitable melting furnace.

The pouring ladle 11 comprises an enlarged bowl 26 constituting a reservoir for the molten metal, and a trough 27 which supports the siphon 12. The ladle also has a skim gate 28. The ladle 11 is supported by a mechanism which permits tilting the ladle to change the elevation of the reservoir with respect to the siphon; raising and lowering the entire ladle without tilting it; and swiveling the entire ladle from a position (see FIG. 2) with the siphon 12 over a slag pot 29 to a position with the siphon over the mold 113.

The supporting mechanism is illustrated somewhat diagrammatically. It comprises an elevator cylinder 31 whose lower end is fixed; cylinder 31 has a piston connected to pedestal carriage 32. Operation of elevator cylinder 31 raises and lowers the entire pedestal carriage 32 as a unit. The pedestal 32 carries an arcuate guide track device 33 on which is movably mounted a ladle carriage 34. Arcuate track 33 is laid out on the arc of a circle whose center is the center of siphon cup 42, and Whose radius is indicated by the dot-dash line in FIG. 1.

The ladle carriage 34 carries rollers 35 which ride on the arcuate guide 33. A tilting cylinder 36 connects with a cross member 37 secured to the pedestal 32; and its piston connects with the ladle carriage 34. The pedestal carriage 32 is rotatable about the vertical axis of elevator cylinder 31 to permit the operator to swing the ladle 11 in a horizontal plane as described above.

Operation of elevator cylinder 31 raises and lowers the ladle 11 without tilting it. Operation of tilting cylinder 36 causes ladle carriage 34 to ride on arcuate track guide 33 and thus to tilt the ladle 1. in a vertical plane about the center of siphon cup 421; this tilting may be accomplished in any position of the ladle 11 in its arc of swing around the vertical axis of elevator cylinder 31, and in any elevation of pedestal carriage 32.

It will be understood that the tip 42 in register with the mold cavity, when the elevator cylinder 31 reaches its lowermost position, the siphon tip 42 is automatically at the proper level within the mold 133 regardless of angle of tilt of the ladle ll. Proper positioning of the tip 42 in the mold causes the tip to be completely submerged in the molten metal when the molten metal occupies its normal position of about 1 /2 inches below the top of the mold. See FIG. 3.

Any operation of the tilting cylinder 36 to tilt the ladle 11 in either direction operates to change the level of the metal in the ladle and, with the pedestal carriage 32 at its lowermost position, does not change the elevation of the tip 42 from its proper position in the mold.

Thus, with the tip 42 in its proper position in the mold, metal level in the ladle ll may be changed either by tilting the ladle, or by adding metal to the ladle or by removing metal from the ladle. The control of metal level in the ladle is used to control rate of metal flow through the siphon 12 as explained hereinafter. The ladle may be tilted backward (i.e. carriage 34 lowered) far enough to stop flow through the siphon.

The manner of conveying molten copper from the holding furnace 10 to the mold 13 will be briefly outlined. The pouring ladle 11 receives the metal stream from the holding furnace it). The ladle bowl 26 is covered with charcoal and it delivers metal from a point near the bottom under the skim gate 28 in the usual manner.

The manner of handling the hot metal will depend on the nature of the metal. In the case of tough pitch copper, for example, the metal stream may fall through air in passing from holding furnace It] to pouring ladle 11. This is generally suitable also for highly deoxidized coppers. However, with all coppers, and particularly with oxygen-free and low residual phosphorous deoxidized coppers, it may be advisable to use a reducing gas here to prevent oxygen adsorption. With phosphorized copper, a cover 23 of carbonaceous material such as flake graphite is maintained on the free surface 24 of the molten metal in the mold, as discussed more in detail below.

During the continuous casting operation, the platform 13 may be lowered at a uniform speed which is variable at will. Accuracy may be maintained within a limit of one percent of constant speed by a special high precision hydraulic system (not shown).

The red hot billet casting, emerging from the mold is rapidly chilled by a series of pressurized water sprays (8% d7, 1EB315) described hereinafter, and the large volume of water is collected in tank 20. This water is removed at any desired level as by a suitable drain line 57. The water may be circulated by a circulation and pumping system, through a cooling device, and back to the Water manifold 7ft on the mold 133 as described hereinafter. The intensity of cooling of mold i3 is so high that, even at the high casting speeds employed, the molten metal congeals practically as soon as it touches the mold wall, causing the edge of the crater shell ltll to extend substantially to the free surface 24.

In the description, certain metals, sizes, values and dimensions are given for purposes of illustration. These are given for convenience of disclosure only, it being understood that the teachings of the invention apply to other metals, sizes, values and dimensions. Unless otherwise indicated, the prior and following description applies to casting phosphorous deoxidized copper circular billets having a nominal diameter of about three inches.

Siphon Referring now to FIGS. 3 to 8, the siphon 12 will now be described more in detail. The siphon 12. comprises a siphon tube 40 having inlet holes 41 constituting a strainer at its back end; a discharge tip or overflow cup 42 at its front end, with an intermediate arched portion therebetween. The siphon 12 is preferably made from stainless steel.

For melting out frozen metal in case of an accidental freeze-up, a special shroud 43 is provided. The shroud is U-shaped in cross section for the greater part of its length (FIGS. 4 and 5) and follows the arched portion of the siphon tube. Its side and bottom walls are provided with anchor pieces 44 which anchor the siphon in the refractory lining 46 of the ladle wall 45'. The side walls of the shroud 43 closely fit the ladle wall lining 46 where the siphon passes through the wall, to prevent loss of liquid metal as discussed below; the shroud 43 is spaced at all sides from the siphon tube 40 as indicated in FIGS. 4 and 5.

To confine the molten metal when the ladle is tilted during a start-up, as described hereinafter, a dam 47 closes the cross section of the shroud as indicated in FIG. 4. The shroud 43 is also provided with a cross piece 48 at its back end for anchoring the shroud relative to the siphon tube.

The forward end of the shroud 43 has an upright front To prevent loss of suction during a starting-up operation, the discharge end of the siphon is provided with the overflow cup 42. The cup 4-2 has a lower discharge opening provided with a steatite washer or nipple 53'. The lower end of the siphon tube 4% has three notches 54 (P16. 7) and has three lugs 55' to which the overflow cup :2 is welded. This construction forms three upper cup overflow openings 56. Thus, provision is made for the siphon to discharge molten metal through both the lower steatite opening 53 and the three upper cup overflow openings ss.

For convenience of explanation, the opening in steatite bushing 53 will sometimes be referred to as lower orifice 53 and the overflow openings 56 will sometimes be referred to as upper orifice 5'6.

One procedure for starting the pouring operation will be, first, only briefly described after which the starting will be described more in detail. The siphon 12 must be first primed; an excess flow rate is required for priming. Before delivering metal to the mold 13 the llow reduced to a volume more suitable for starting the ct operation. Then the siphon cup 42 is registered over the mold l3 and lowered into the mold. When the mold fills and the metal covers the cup, the operator starts downward movement of the starting plug it? at reduced starting speed. The reduced priming flow rate automatically decreases, when the cup becomes submerged, to a rate corresponding to the lowering rate of the starting plug 1?. operator then increases the lowering rate of the start plug to full running speed and at the same time raises the liquid level in the ladle to provide sufficient head to deliver metal at the increased rate.

The starting procedure will now be described more in detail. Because of the small volume of a 3 inch billet mold and because it is desired to employ a high casting rate, special precautions must be taken both in starting up and in maintaining normal running conditions.

As stated, the casting operation is first started reduced pre-set rate after which the casting rate is increased to normal running speed. in a full size pilot plant operation, successful casts were made at normal running speeds as high as 90 pounds per minute; this is equivalent to a linear billet casting speed of about 40 in per minute in a 3 inch billet mold. As discussed below, data obtained from tests in the pilot plant indicated that running speeds considerably in excess of 90 pounds (40 inches) per minute are entirely feasible by practice of the invention.

With normal running speeds of about 90 pounds per minute, a suitable reduced pre-set starting rate was found to be about pounds per minute, which equivalent to a linear billet casting speed of about 20 inches per minute. The 20 inches per minute pre-set speed is only comfortably above minimum casting speed below which it is im possible to cast with the mold having the large angle or forced taper discussed below and claimed in the parent case.

As the first step in the starting procedure. the entire siphon assembly i2 is preheated by a heating torch to bright red heat approaching the melting point of copper to prevent accidental freeze-up. It will be understood that, in order to prime the siphon and establish stable flow conditions, as much as several hundred pounds of molten copper may be run into a separate container; priming is therefore done with the ladle l1 pushed around to the position shown in dot and dash lines in FIG. 2, where siphon 12 can discharge into slag pot 29.

To prime the siphon, the holding furnace ill is tipped and metal is poured into the ladle 11. When the ladle is nearly full of copper, it is tilted forward, causing the molten metal to flow toward the siphon 12-. The ladle is tilted enough to bring the molten metal level higher than the highest part of the arched siphon tube 4% the dam 47 serving to retain the molten metal. This supplies a hydrostatic head to the siphon tube 40 and produces a copious metal flow through lower orifice 53 and upper orifice 55.

After the siphon has been primed, the ladle is tilted backward to reduce the priming flow to a rate suitable for starting; this will be greater than the above-mentioned pre-set reduced starting rate. With the apparatus used in tests, a free flowing pouring rate of about 60 pounds er minute proved satisfactory. This rate could be checked visually very easily; when the flow from the top orifice 56 was reduced to an intermittent, or very small, trickle (while full flow from the bottom orifice'53 continned), proper pouring rate was indicated.

Having adjusted the ladle to discharge at the free pouring rate of 60 pounds per minute, the ladle 11 is then raised if necessary to clear the mold 13 (but without changing the angle of tilt). Then, with metal still flowing, the siphon 1.2 is swung about the vertical axis of pedestal carriage 32 from over slag put 29 to register over mold l3, and the tip 42 is rapidly lowered into the mold cavity (again without changing the angle of tilt) until the pedestal carriage 32 reaches its lowermost point. This places the siphon tip 42 at proper level in the mold.

With the above-mentioned free pouring rate of 60 pounds per minute from steatite orifice 53, a period of about 10 to 12 seconds is about all the time that can be allowed, after registration of the siphon tip 42 with the mold cavity, in which to lower the siphon 12 into the mold and to start downward movement of the starting plug 17, without overfilling the 3 inch billet mold.

As soon as siphon tip 42 is in line with the mold 13, the mold starts filling with molten metal; and when the level in the mold reaches normal level of about 1 /2 inches below the top of the mold (above the top of siphon cup 42 the operator starts the lowering mechanism to withdraw the starting plug 17 at the pre-set rate of 20 inches (45 pounds) per minute.

With the ladle tilt angle adjusted to give this free pouring rate of 60 pounds per minute, the construction is such that, with the ladle originally filled to the proper level, the level of molten metal in the ladle ll will be automatically located no higher than about /2 inch below the top of the mold 13 when the pedestal carriage 32 reaches lowermost position. This is the ladle position and molten metal level illustrated in FIG. 1.

This constitutes a safety device since, if the starting plug 17 is not lowered out of the mold soon enough, the molten metal in the mold can rise only to the same level as the level in the ladle (which is about /2 inch below the top of the mold) and thus cannot overflow the mold.

When the molten metal level in the mold rises to above the top of siphon cup 42, the rate of flow through the siphon automatically decreases to a rate corresponding to the rate at which the starting plug 17 is withdrawn. The flow rate being proportional to the square root of the difference in head, the metal level in the mold will rise until the difference in head corresponds to the withdrawal rate of the starting plug.

The operator may continue pouring and withdrawing at the pre-set reduced starting rate of 20 inches (45 pounds) per minute until he is sure everything is in or der. When the operator is ready, he then tilts the ladle it forward, or adds metal to the ladle from the holding furnace it to raise the molten metal level in the ladle to about /2 inch above the top of the mold; this increases the pouring rate to the normal running rate of pounds per minute. This position is illustrated in FIG. 3. At the same time that the operator increases the pouring rate to 90 pounds per minute, he increases the downward velocity of the starting plug 17 to the corresponding casting speed of 40 inches per minute.

The metal level in the mold then reaches equilibrium about 1 /2 inch below the top of the mold. It was found that, with the siphon used in tests, about a 2 inch head of metal was required for a flow rate of 90 pounds per minute through the siphon.

In the following discussion, it will be understood that by effective area is meant the area which controls the rate of flow through the several parts of the siphon, namely, the siphon tube 40, the lower discharge orifice 53 and the overflow orifice 56.

The effective area of the bottom orifice 53 is governed by the flow rate desired by the operator for the particular mold and the desired starting conditions. There is a definite relationship between the effective areas of the bottom orifice 53 and of the cross section of the siphon tube t-tl in order to build up sufficient velocity head in the cup 42 to keep the level of molten metal in cup 4-2 above the end of the siphon tube during priming. The combined effective area of the overflow orifice 56 and bottom orifice 53 is preferably greater than the effective cross sectional area of the siphon tube 40, so that maximum flow and velocity are obtained in the tube 40 in order to flush out gases. If the lower orifice 53 is too small, the velocity through the siphon tube will be too low, allowing gas separation at the top of the arch of the siphon tube and loss of siphoning action or possible freezing of the metal in the siphon tube.

For example, in a siphon for feeding a three inch billet mold, it was necessary to limit the size of the bottom orifice 53 to no greater than 80% of the effective area of the siphon tube 40. The best operating ratio was found to be between 30% and 60%. The effective area of the overflow orifice 56 should be no less than 50% of the effective siphon tube area, but no critical relation exists here since the main function of these ports is to assist in obtaining easy priming by rapidly flushing the trapped gases from the siphon tube. It therefore follows that the sum of the effective areas of the lower orifice 53 and of the overflow orifice 56 should be nearly equal to (not less than 80%), or preferably greater than, the effective area of the siphon tube 40.

It will be understood that, if the lower discharge orifice 53 is too small, the flow through the siphon will not be fast eonugh to flush entrapped gases from the siphon tube. The cross section of the siphon tube at the top of its arch must be small enough to cause the velocity at this point to be sufficiently high to prevent entrapped gases from collecting. On the other hand, there must be sufficient flow through the overflow orifice 56 to seal the end of the siphon conduit, particularly when the molten metal does not wet the metal of the siphon conduit.

It is important too that the area of bottom orifice 53 be accurately maintained; it has been found that the steatite washer 53 withstands the wearing action of hot molten copper very well so that the starting flow rate, when once established at the desired value, can be reliably maintained.

With high linear billet withdrawal rates of the order of 3 feet to 40 inches and higher per minute, very accurate pouring control and withdrawal control is necessary.

For uniform mold casting conditions, the free metal level in the mold should be held to less than plus or minus 1 inch (preferably within plus or minus /2 inch) from normal level; normal level is about 1%. inches below the top of the mold.

Furthermore, to prevent inclusion of the carbonaceous mold cover 23 in the surface of the casting, the metal level must be kept above the top of the siphon cup 42; also, the metal level must not change too rapidly or else the carbonaceous cover adhering to the mold wall (on top of the metal surface at the meniscus) will be cast into the surface of the molten metal if it rism rapidly. A slow rate of rise is apparently not harmful since the reciprocation of the mold works any excess of carbonaceous cover away from the meniscus if given a finite time of about 30 seconds.

To obtain accurate pouring control, the ladle body 11 t has a horizontal area many times the cross sectional area of the mold cavity. For example, in pilot plant operations, the ladle body had a horizontal area of over 300 square inches as compared with the cross sectional area of the 3 inch billet mold which is about 7 square inches. This represents a ratio of over forty to one. This means that each 1 inch of metal depth in the ladle contains about 100 pounds of metal, in contrast to about 2% pounds for each 1 inch of metal depth in the mold.

It will be apparent that any given variation in pouring rate from furnace It? into the ladle ll will cause a much less change in level than the same variation would cause if applied directly to the billet mold. This follows be cause the ladle acts as a sort of large area reservoir which can absorb relatively large variations in supply without materially affecting molten metal level.

For example, an increase, in the normal 99 pounds per minute pouring rate into the mold, by as little as 2% pounds per minute would raise the liquid level in the 3 inch billet mold by 1 inch in 1 minute (or /2 inch in 30 seconds), assuming cast billet withdrawal speed to be held constant at 4-0 inches per minute. On the other hand, to cause an equivalent rise in level in the ladle, an increase, in the normal pounds per minute pouring rate from holding furnace 10 to ladle ll, of as much as 100 pounds per minute would have to occur.

As shown above, there is no problem in accurately controlling the liquid level in the ladle 11. Thus, with liquid level in the ladle and the billet withdrawal speed both maintained approximately constant, the liquid level in the mold must stay within the permissible limits. The pouring and withdrawal apparatus has a built-in automatic correction device in that, if the liquid level in the mold rises, the liquid head automatically decreases, thus decreasing metal flow; on the other hand, if the liquid level in the mold drops, the liquid head automatically increases, thus increasing metal flow.

The operation of the shroud in case of a freeze-up will now be described.

The function of the shroud 43 and overflow holes 51 and 52 is to remelt a frozen siphon tube 4t Due to error in preheating causing freeze-up, or in event of a foreign body becoming lodged in the siphon tube, the flow of copper during priming may cease before full metal flow can be established. If this condition occurs, the ladle is tilted to an elevation permitting molten metal to flow over the dam 47 and around the siphon tube.

Freezing can also occur between the shroud 43 and the tube 40, and progressive melting is required to remelt this metal. This is accomplished by allowing the molten metal to overflow the front wall 49 of the shroud 43 and flow, in succession, from the holes 51 and 52 in the front of the shroud. The frozen metal is quite rapidly remelted and in a few minutes any frozen area in the siphon tube becomes remelted and flow conditions are established.

I briefly discuss some of the difficulties overcome by the overflow cup 42 as shown in tests. Without the cup, it would be necessary to establish an undesirable high flow rate through the siphon for priming and starting. Upon reducing the head of metal in the ladle to produce a lesser and more desirable stream velocity, the heavy liquid copper would run down one side of the siphon tube and allow air to enter the opposite side of the tube, breakmg the siphoning action. A new siphon tube can usually be started without cup 42 due to the wetting effect of the copper on the clean surface of the high chrome-iron tube, but, in general, with an oxidized surface, the ability to get started Without the cup was unreliable. It will be understood that this difficulty is associated only with priming the siphon and starting the casting operation.

After the siphon tip is once submerged in the molten metal in the mold and kept there, a steady and controlled flow is easily maintained. Under these conditions the cup then serves the additional purpose of distributing the metal through both its upper and lower orifices. It is desirable to balance this distribution because a disadvantageously long V crater is created when all of the hot metal is delivcred downwardly at the center.

Mold The mounting for mold 13 will now be described (FIG.

c eeses l). The mold is supported on carriage 15 having four Wheels of riding on two rails 16; thus the entire mold may be rolled out of the way to give access to the top of tank 29 in the casting pit and to the hydraulic mechanism for the removal of the cast product, after pouring operation is completed.

The mold 13 is supported by a frame 1 Which is vertically oscillated by a reciprocating mechanism. A suitable prime mover (omitted for simplicity) is mounted on carriage 15', which reciprocates connecting rod 61. Rod 61 is pivoted to a series of hell crank levers 62 on one side of the frame 14. A series of hell crank levers 53 are pivoted to the carriage on the other side of frame .14. Links 64 and 65 pivotally connect bell crank levers ll and 4t to oscillatory frame 14. A connecting rod 66 connects bell crank levers 62 and 63. A series of guide posts 67 are supported on carriage 153, and slidably engage guides on frame to insure vertical reciprocation of the mold in a substantially vertical straight line.

Any suitable means may be provided to vary stroke and frequency of vertical reciprocation of the mold. For example, to vary stroke, the drive motor may have a crank arm whose length is adjustable. To vary frequency, motor speed may be changed.

When casting coppers free of oxygen, it is desired to protect surface of the liquid metal from contact with oxyge. A preferred method, in the case of phosphorous deoxidized copper, is to use a graphite flake cover 23 on the top of the molten metal in the mold. The reciprocating action of the mold works the graphite flal es down the mold wall where they finally emerge at the bottom and are washed away by the water sprays. However, other carbonaceous materials may be used, and for some purposes, air displacement by a non-oxidizing gas is all that is necessary.

Referring more particularly to FIGS. 9, l and 11, the mold 13 will now be described.

The mold l3 comprises a composite graphite block supported in a metal frame comprising a bottom annular manifold and a circular sleeve '71. The sleeve 71 has a bottom ring 72 welded thereto which ring is bolted to the manifold at The frame has a top annular plate 74- covering the ends of the cooling tubes r33. Bolts 75 secure this plate to a ring as which is welded to sleeve 75L. The manifold '74 rests on suitable cross pieces forming part of platform 3. reciprocataoly mounted on carriage 15.

As shown in FlGS. 9 and 10, the graphite blocl; comprises a main block '79 having upper and lower removable sleeves or liners 94, Q5. The graphite block '79 and sleeves We, 25 are made from suitable commercial graphite and are machined to the shape indicated.

The sleeves 9d, 5 5 are removable mainly to facilitate repair of the mold in case the molding surface is damaged. lf desired, the sleeves may be omitted and the graphite block made unitary, with the molding surface 319 machined directly into the main block as illustrated in FIG. l.

The interior mold surface 88 is machined to vary from a true cylinder in the taper hereinafter discussed. Both sleeves 9-3, d5 carry the taper and the lower sleeve also carries the water passages and supporting ribs 92 as here inafter described.

In order to obtain optimum heat transfer, the sleeves 94 and 95 must be carefully fitted into the main block 79. The contacting surfaces are cylindrical and are carefully machined so that solid-to-solid contact is obtained between sleeve and block without any fluid layer at the interface which will interfere with excellent heat transfer.

The sleeves 94, d5 are preferably made oversize with respect to the block. The sleeves are assembled into the block by forcing the sleeves axially into the block.

The compression fit between main block and sleeves must be sufficiently severe to obtain the solid-to-solid, fluid-free contact at operatingtemperatures. Since the sleeves and block are made of the same material, and

i sincethe sleeves will run at a higher operating temperature than the block, good thermal contact is positively maintained during the casting operation.

A tight fit is desirable also between the graphite block 79 and outer steel jacket if, to properly reinforce the frangible graphite against the disruptive forces caused by the expandible coolin tubes 83 and by operation of the forced taper described hereinafter. To obtain such tight fit, the outer sleeve 7'1 is preferably made slightly smaller than the graphite block 79. The metal sleeve '71 is heated and shrunk onto the graphite block; or these members may be axially forced together.

The manifold 76 is annular. At its upper and inner corner is an extension ledge 31 facing the interior of the mold. The manifold I'll has an inlet passage 82 having a flange for connection with a pipe (not shown) which supplies the manifold with cold water. Additional inlet passages located at equidistant points on the annular manifold may be provided, if desired, for the large quantitles of Water supplied to the mold.

The manifold id delivers wateto the main cooling tubes 33 and to live levels of Water sprays. For this purpose the manifold has a series of top holes 34; a series of bottom holes 85; its ledge til has a series of drilled passages as; the ledge contains holes '78 to clear the main cooling tubes 33.

The water delivery to the top or first level sprays will now be described. The graphite block *2? has a series of horizontal radial passages containing cross tubes 88. Each. cross tube has a nozzle tip 255* having a downwardly directed discharge passage disposed at a 29 angle to the vertical. The cross tubes connect with elbows 9b which are connected to fittings 91 connected to the top holes 84 in the manifold '79.

it will be noted that the inner face of the lower sleeve 95 has clearance bays below the discharge nozzles $9 providing, in effect, vertical ribs which are available to support the casting While the Water sprays are directed between the ribs onto the surface of the casting before it leaves the mold; this insures cooling the surface of the casting below the plastic range while so supported.

The second level of sprays is provided by nozzle holes 87 rilled into the ledge 81 and connecting with the passages 36 in the manifold. The axes of the nozzle holes $7 may have an angle with the vertical of about 20.

The third, fourth and fifth levels of sprays are provided by openings Th3, Mid and located in cooling tubes 96 and in the return bends All of these spray openings direct water against the emerging casting in the directions indicated by the arrows. The return bends Q3 connect lower openings with inner tubes 96.

The main cooling tubes will now be described. The outer cooling tubes 33 are loosely disposed in the upper ends of openings '78 in the ledge 31, and have special fits with the drilled and reamed openings in the graphite block "id through which they pass. The inner tubes as are disposed inside of the outer tubes 83 and extend short of the top of the outer tubes. The outer tubes 33 have top caps 9'7 silver soldered thereto.

The outer cooling tube 83 has a normal size which is oversize with respect to the opening in the graphite 79 in which it fits. The outer tube 83 is provided with an inner longitudinal rib @S (Flu. 11) which limits the force exerted by the copper tube on the graphite when the copper tube is forced into the graphite block and also when the tube expands from heat under casting conditions.

The inner tube 96 has two longitudinal external ribs J9 and a longitudinal internal rib res. Internal rib l'dd surrounds internal rib 98, and the external ribs d9 space the inner tube from the outer tube to form the water passages illustrated particularly in the drawing.

The relationship between the cooling tubes and the graphite blocks is most important. The outer copper tubes 83 are fitted oversize in the drilled and precisely reamed graphite holes at room temperature. The tubes being of copper will expand more than the graphite mold block at casting temperatures and thus improve initial contact pressure during the service period.

The longitudinal expansion rib 98 avoids placing undue stress on the graphite since the expansion of the tube is accommodated by elastic collapse of the rib under compression and thus the copper tube maintains the desired surface-to-surface fit with the graphite 79.

Thus, a great volume of water is fed into the lower ends of the inner tubes 96, which water overflows at the upper ends of the inner tubes and passes down between the tubes 83, 96, as indicated by the arrows. in order to obtain maximum heat transfer, the ribbed side of the outer tube 83 faces the outer side of the mold wall so that the circular side faces the mold surface liners. The fit of the inner tube 96 within the outer tube 83 determines the dimensions of the return passage for the water which is shaped to provide maximum water flow over the smooth surface facing the molding space, and minimum flow on the back side. These provisions accomplish both high velocity flow and economy of water, while providing maximum cooling eficiency.

The details of construction and fit of the inner and outer cooling tubes 83, 9-6, the manner of connecting the various bends and elbows for the sprays, form no part of the present invention. For details of these and for other detail of the mold, reference is made to prior application, Serial No. 606,518, filed August 27, 1956, in the names of Richard Baier, John Stuart Smart, lit, and Albert]. Phillips.

There are certain inherent advantages in a circular arrangement of cooling tubes and outer shell. The natural stress reinforcement afforded by the outer shell 71 permits placing the expandable cooling tubes 83 closer to each other, and closer to the mold cavity, without danger of fracturing the graphite. The circular outer sleeve '71 reinforces the mold also against the fracturing pressures caused by the forced taper as discussed below and in the parent case.

It will be understood that the advantages of the circular shape applies also to those non-circular casting cavities which do not depart too much from circular, that is, which have cross sections more or less symmetrical around a longitudinal axis with respect to radial heat transfer; as, for example, equilateral triangle, square, hexagon, octagon, and even an oblong which does not depart too much from square.

The above statement applies not only to the tensile reinforcement afforded by the outer shell '71 to stresses caused by the expandable cooling tubes, but also to stresses applied by the forced taper operation discussed below.

Forced Taper The mold pocket wall 80' is especially tapered. It is provided with what may be called for convenience a forced taper, to distinguish it from prior art tapers which may be called natural tapers. in a word, I so relate the steepness of taper to linear casting speed that I forcibly wedge the shrinkage taper on the cast product against the taper on the mold pocket so as to to plastically dc form the red hot tube comprising the crater shell enclo ing the liquid core.

The forced taper operation, in a sense, is similar to wiredrawing. It requires the establishment of a crater shell with a long and deep V, with a strong but plastic shell wall surrounding a soft liquid center, a combination that is readily deformed by pulling it through the tapered mold. Weak and thin shells must be avoided because they merely tear apart. Shallow \is that are formed by casting at low speeds, as described in the prior art, are not sufficiently plastic and will hang up in the tapered mold rather than deform. The combination of mold design factors and operating technique needed to accomplish the desired result will be more readily apparent from the following discussion.

It will be understood that a natural taper can be designed to follow the shrinkage pattern of the casting, as it passes through the mold, rather closely at any particular linear billet speed; a slow linear casting rate which produces a well cooled cross section permits the use of a steeper mold taper (i.e. at a larger angle to vertical) than a rapid linear casting rate where the shape is emerging from the mold at a higher temperature, but in either case precaution must be taken to prevent hang up, which re- :sults from the use of excessive tapers in molds constructed and operated according to the prior art. Accordingly, with natural tapers, a small but finite clearance is necessary between the billet and mold Wall along the major length of contact in such molds.

The forced taper of the present invention depends on the discovery that the natural taper can be greatly exceeded by creating a freezing zone capable of easy deformation along its entire length of contact with the mold wall, while simultaneously employing the forced contact to improve the rate of heat extraction from the shell to mold wall to such a degree that the shell wall congeals sufficiently strong and thick to resist rupture at the high operating speed necessary to create the deep V required.

The invention may be employed to cast any metal or alloy, such as steel, silver, nickel, aluminum, magnesium and particularly copper. It is especially useful for casting oxygen-bearing copper such as tough pitch copper in any desired size; and for casting coppers free of oxygen such as oxygen-free or phosphorous deoxidized copper.

The term oxygen-bearing copper, as used herein, is intended to include tough pitch copper as well as copper containing a lesser amount of oxygen; it is intended to include any copper in which oxygen is in available form for attacking the graphite if the reaction temperature of the graphite is exceeded.

On the other hand, the term copper free of oxygen, as used herein, is intended to cover those coppers known as phosphorous deoxidized copper containing both high phosphorous and low residual phosphorous, any other deoxidized copper such as copper deoxidized by lithium, boron, calcium, etc., and also those coppers referred to as oxygen free; in other words, any copper in which there is no oxygen available for attacking the graphite at its reaction temperature.

For casting coppers free of oxygen, it is preferred to introduce a protective layer 23 (FIG. 3) of discrete particles of carbonaceous material, such as flake graphite, lamp black, pulverized anthracite, etc., floating on the surface of the molten metal in the mold. A mixture of flake graphite and fine carbon particles known as Micronex was used quite sucessfully in tests. This was spooned in on top of the free molten surface in the mold from time to time, to maintain the blanket.

This cover acts as a protective blanket to prevent oxygen absorption and also prevents build-up of phosphate slag or other extraneous material on the mold wall. Reciprocation has a special purpose when casting coppers of this type, since it also feeds a controlled film of carbonaceous material between the mold and casting, resulting in a superior cast surface.

Oxygen bearing coppers act decidedly differently. Here,

reactive carbon produces defects, and the use of a bare mold wall is preferable to the nuisance of trying to apply an inert mold dressing and maintaining a uniform coating at all times.

The amplitude and the frequency of reciprocation of the mold is related to the cross section being cast, the amount of taper and the casting rate. In general, I have found that the ratio or reciprocation frequency (in number of cycles per minute), to casting speed (in inches per minute), should be about eight or ten to one, with an amplitude of 2 mm. (.08 inch). That is to say, cycles per minute at a linear casting rate of 20 inches per minute, or 350 cycles per minute at a linear casting rate of 40 inches per minute. A short stroke is generally to be preferred since this avoids excessive clearance be- 13 tween mold and casting on the downward portion of the stroke.

By stroke or cycle is meant a complete round trip movement of the mold from bottom position back to bottom position. The movement is substantially simple harmonic. varying from zero speed at upper and lower ends to maximum speed between the upper and lower ends of the amplitude of movement.

It is desired that the maximum instantaneous speed of the mold be gerater than the uniform linear speed of the billet to provide a small gap between mold taper and casting taper and thus to permit a certain amount of the cover 23 to feed down the mold wall between mold and cast product.

While certain novel features of the invention have been disclosed herein, and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. In a system of continuous casting comprising a mold having a cavity with an open top, a starting plug disposed in said cavity, a ladle having a reservoir to receive metal, a siphon having an inlet communicating with said reservoir and a discharge tip projecting from the ladle, means for tilting the ladle, means for raising and lowering the ladle, and means for swinging said ladle about an upright axis, the method of starting a pouring operation which comprises filling the ladle with molten metal to the desired level, tilting the ladle forward to start the metal flowing through the siphon into a waste pot, tilting the ladle backward to obtain true siphoning action and to reduce flow, swinging the ladle, without substantially changing the angle of tilt, to register its tip with said mold cavity, lowering the tip into the mold cavity without substantially changing the angle of tilt, and Withdrawing the starting plug and embryo cast product at a velocity corresponding to the starting rate, changing the level of metal in said ladle to increase the pouring rate, and increasing the velocity of withdrawal of the cast product to correspond to the increased pouring rate.

2. The method of insuring continuity of metal discharge from a siphon which discharges a free falling metal stream under siphoning conditions wherein the metal does not wet the surface of the siphon passage, said method comprising establishing said free falling metal stream and placing the discharge end of the siphon passage under suflicient static head to seal the siphon against leakage of gaseous arnbient, notwithstanding the tendency of the molten metal to run down one side of the siphon passage.

3. In a system for continuous casting, a mold having an open top and open bottom, a ladle having a reservoir to receive molten metal, a siphon mounted on said ladle, said siphon having an inlet communicating with said reservoir, and a discharge tip projecting from said ladle, a support, means mounting said ladle on said support so as to pivot said ladle relative to said support about the vicinity of said discharge tip as a center, means for raising and lowering said support through a range of movement sufiicient to place said discharge tip above and below and within the top of the mold, stop means for limiting downward movement of said support when said tip is disposed a predetermined distance below the top of the mold.

4. In a system according to claim 3, means for swinging said support about an upright axis selectively to bring said siphon tip into or out of register with said mold.

5. In a continuous casting process wherein molten metal is fed from a reservoir through a siphon into a mold cavity, and wherein a starting plug is disposed in said cavity, the method of starting the pouring operation, which comprises raising the level of molten metal in said reservoir above the siphon to cause a copious flow through the siphon and to thereby prime the siphon while delivering the metal to waste, lowering the metal level in said reservoir below the arch of the siphon while placing the discharge tip of the siphon passage under sufflcient static head to seal the siphon against ingress of gaseous ambient and delivering the free falling stream of metal of waste, then directing the free falling metal stream into the top of the mold, and withdrawing the starting plug after the metal level in the mold rises to the desired level.

6. In a system of continuous casting which comprises a mold having a cavity with an open top and an open bottom, a starting plug disposed in said cavity, a unit comprising a ladle having a reservoir to receive metal and a siphon having an inlet communicating with said reservoir and having a discharge end projecting from the ladle; the method of starting the pouring operation which comprises feeding molten metal to said reservoir, tilting the unit forward to bring the metal level in the ladle above the arch of the siphon to prime the siphon while directing the discharge to waste, tilting the unit backward to lower the metal level in said reservoir with respect to the siphon to obtain true siphoning action and to reduce the flow rate through the siphon while directing the discharge to waste, then directing the discharge of the siphon into the mold and withdrawing the cast product when the molten metal in the mold reaches a level above the discharge of the siphon.

7. In a device for pouring molten metal, a ladle having a reservoir to receive metal, a siphon having an inlet communicating with the reservoir and a discharge end projecting from the ladle, means for tilting the ladle to raise and lower the reservoir with respect to said discharge end, a shroud built in the wall of the ladle, said shroud comprising a channel surrounding the arch of the siphon and communicating with said reservoir, said shroud having a darn closing the space between said channel and siphon, said dam serving to stop the flow of metal when the ladle is tilted sufliciently to prime the siphon, said dam having an overflow surface below the adjacent channel wall over which metal flows when the ladle is still further tilted to melt out a frozen siphon, said metal flowing between said siphon and channel to melt out a frozen siphon.

8. In a continuous casting process wherein molten metal is fed from a reservoir through a siphon into the cavity of the mold and wherein a starting plug is disposed in said cavity, the method of starting the pouring operation which comprises priming the siphon and delivering the metal away from the mold, then flowing metal through said siphon into the mold, establishing a molten metal level in said reservoir below the top of the mold, withdrawing the starting plug and embryo cast product when the metal reaches proper level in the mold, thereafter, raising the molten metal level in the reservoir to above the top of the mold to increase the pouring rate, and increasing the velocity of withdrawal of the cast product to correspond to the increased pouring rate.

9. In a continuous casting system which comprises a reservoir for holding molten metal, a mold having a cavity with an open top and bottom, a starting plug disposed in the mold cavity, a siphon having an inlet disposed in said reservoir and a discharge end projecting from the reservoir, said discharge end having an overflow cup, said discharge end having an overflow opening and a bottom opening; the method of starting a pouring operation which comprises raising the level of molten metal in the reservoir above the arch of the siphon to prime the siphon, lowering the metal level in said reservoir below the arch of the siphon to obtain true siphoning action at such rate as to maintain the overflow cup SllfilClClJflY full of molten metal to seal the siphon against ingress of gaseous ambient while flowing metal from said discharge end in a free falling stream from a point above the mold, directing the free falling metal stream into the top of the mold cavity, lowering the discharge end of the siphon into the mold to immerse 15 the overflow cup in the molten crater of the embryo casting and thereby to distribute the metal delivered to the crater, and withdrawing the starting plug after the metal in the mold rises to the desired level.

References Cited in the file of this patent 5 UNITED STATES PATENTS 6 Iunghans Dec. 15, 1942 Ennor et al July 13, 1954 Schnacke June 23, 1959 Gerster July 7, 1959 Baier et al July 26, 1960 FOREIGN PATENTS Germany Oct. 6, 1955 Australia Feb. 29, 1958 

